Method of producing a bright finish



United States Patent METHOD OF PRODUCING A BRIGHT FINISH ON STAINLESSSTEEL Sidney Livingston, Beechhurst, and Leonard Mackles,

New York, N.Y., assignors to Chemclean Products Corporation, CollegePoint, N.Y., a corporation of New York No Drawing. Filed Aug. 24, 1960,Ser. No. 51,498

1 Claim. (Cl. 156-20) This invention relates to a method of producing abright mirror-like finish on stainless steel by chemical means.

Various methods are now available for polishing stainless steel by theuse of chemical preparations in combination with electric current. Thesemethods are commonly designated by the term electropolishing and arefully covered in patent and trade literature. Also known and used aremechanical polishing methods, either alone or in combination withchemical or electrochemical means.

The principal object of the invention is the provision of a purelychemical method of producing a bright mirrorlike finish on stainlesssteel, said method involving the use of chemical means alone, producinga purely chemical action, and without the use of electric current.

Microscopic inspection of a typical stainless steel surface prior topolishing will show it to be most irregular and consisting of aplurality of high spots or projections interspersed among a plurality oflow spots or depressions. Even the high spots may themselves be formedwith depressed points or areas and similarly the low spots maythemselves be peppered with high spots or projections. It is thefunction of the method herein described and claimed and of the chemicalmeans involved therein to eliminate or at least soften theseirregularities by selectively dissolving and removing the high spots,while at the same time inhibiting or preventing a corresponding attackupon the low spots, thereby leveling and smoothing the metal surfaceundergoing treatment and producing a bright mirror-like finish.

More specifically, the polishing method herein described and claimedinvolves the use of a chemical composition consisting of dilutephosphoric, hydrochloric and nitric acid combined with an inhibitingagent or restrainer and an activator or catalyst. When stainless steelis exposed to a heated bath consisting of such chemical composition, theresult is a mirror-like finish which is at least as bright as thatproduced by electropolishing. The term stainless steel as used herein isintended to refer to austenitic stainless steel as described, forexample, in the Mechanical Engineers Handbook, fourth edition, edited byLionel S. Marks, page 587.

It has been found that a chemical composition of the following formulaand within the following range of proportions will best perform thefunction and produce the best results herein described:

Percent by weight Phosphoric acid, approximately 15-50 Hydrochloricacid, approximately 2-25 Nitric acid, approximately 1-17 Water,approximately 30-80 Inhibitor, approximately .05-6 Activator,approximately .05-6

Total 100 3,125,475 Patented Mar. 17, 1964 'ice The phosphoric,hydrochloric and nitric acids in dilute form will dissolve the highspots or projections on the stainless steel surface. The inhibitor willprevent or at least inhibit corresponding reaction with the low spots ordepressions in the metal surface. In order to activate the abovecombination and hasten the results, an activator or catalyst is added asabove indicated.

More specifically, an inhibitor of the chemical classification known asacetylene alcohols will function effectively in the combination abovedescribed. An activator of the chemical configuration of formateselected from the aldehyde and acid groups functions effectively as acatalyst in the above combination.

To be even more specific, a suitable inhibiting agent may be selectedfrom the class consisting of monoand poly-hydric acetylene alcohols.Effective inhibiting agents have been found to be 2-butyne-1,4-diol and2-propynl-ol. Suitable activator or catalysts may be selected from theorganic aldehydes and acids of the formic group. Specifically,activators which effectively serve as catalysts in the combinationherein described and claimed are formaldehyde and formic acid.

A specific formula found to be highly suitable for purposes of thepresent invention is the following:

Water, approximately 65 Inhibiting agent, approximately .05 Activatorcatalyst, approximately .05

In the foregoing formula the preferred inhibiting agents are selectedfrom the class consisting of the monoand poly-hydric acetylene alcoholsand particularly 2-butyne- 1,4-diol and 2-propyn-l-ol. Also in saidformula the preferred activator catalyst is selected from the organicaldehydes and acids of the formic group and especially formaldehyde andformic acid.

When the combination of materials above described is put in the form ofa bath and heated to a temperature of approximately -212 degreesFahrenheit, it may be used to produce a bright mirror-like surface onstainless steel. This may be accomplished by immersing the stainlesssteel in said bath for a period of approximately one to thirty minutes.When removed from the bath following such immersion, the stainless steelexhibits the desired finish. Optimum results are attained, however,Within a temperature range of approximately -200 degrees Fahrenheit andwith an immersion period of approximate- 1y one to five minutes.

The foregoing represents preferred embodiments of the present inventionand it will be understood that variations and modifications may beincorporated therein within the broad principles of the invention andthe scope of the claim.

We claim:

A method of treating austenitic stainless steel to produce a brightmirror-like surface thereon, which comprises immersing a stainless steelsurface in a bath consisting of approximately 25 parts by weight ofphosphoric acid, approximately 7.5 parts by weight of hydrochloric acid,approximately 2.5 parts by weight of nitric acid, approximately 65 partsby weight of water, approximately A 3 4 .05-6 parts by Weight of aninhibiting agent consisting of References Cited in the file of thispatent 2-butyne-L4-diol combined With 2-propyn-1-0l, and ap- UNITEDSTATES PATENTS proximately .05-6 parts by weight of an activatorcatalyst selected from the formates, said bath being heated to 2493327 Y32 and maintained at an elevated temperature of approxi- 5 2662814Wlhart 1 mately 190200 degrees Fahrenheit, and said stainless 2993862Monroe et a y 19 1 steel surface being immersed in said heated bath for9. OTHER REFERENCES Period of approxlmately one to five mmutes' Forsteret a1.: Acetylenic Corrosion Inhibitors, Ind. &

Eng. Chem., vol. 51, No. 7, July 1959, pp. 825828.

